This invention discloses compositions adapted to produce, through solid imaging means, excellent quality objects having material properties that simulate the look and feel of polyethylene articles.

This invention discloses compositions adapted to produce, through solid imaging means, excellent quality objects having material properties that simulate the look and feel of polyethylene articles.
In the field of liquid-based solid imaging, alternatively known as stereolithography, compositions have been developed which are capable of generating solid objects having the properties of epoxies and/or acrylates. Solid imaging generated objects made from previous epoxy and/or acrylate compositions provided a prototypical representation of the physical shape of plastic articles made on a production basis out of materials such as ABS, nylon, polyethylene, polypropylene, etc. However, such compositions lack the material properties that give users of the prototypes a sense of look and feel for the object when produced in the production material. Such a lack of look and feel accuracy in product prototyping is not just an aesthetic issue. The look and feel of a prototype also has significant engineering, design, packaging, labeling, and advertising implications.
For example, squeeze bottles, such as those used for dispensing dish soap, are designed to be attractive in shape, easy to grasp, and easy to squeeze. Typically such bottles are made from polyethylene type polymers. Previous epoxy and/or acrylate compositions used in solid imaging were capable of producing articles that have the same attractive shape. However, the stiffness of the prototyped articles made from these materials was likely to mislead the designer and evaluator of the article relative to such issues as, for example, wall thickness and surface radius design. For example, a commercial solid imaging resin, Somos(copyright) 2100 (E. I. DuPont De Nemours, Inc., Wilmington, Del.), produces articles having lower stiffness than polyethylene. Bottles made from this material do not provide adequate resistance to squeezing such that enough friction occurs between a person""s fingers and the bottle. A person holding a Somos(copyright) 2100 prototype bottle of liquid soap is likely to squeeze too hard in order to generate enough friction to keep the bottle from slipping. As a consequence, the soap is likely to be dispensed prematurely. The designer of the bottle might then be misled into making the wall thickness of the bottle greater in order to improve its stiffness. But such a design change would lead to a bottle that is too stiff when manufactured with polyethylene. Similar problems are generated when other much stiffer epoxy and/or acrylate compositions are used to prototype articles such as bottles. A designer might be led to decrease the wall thickness of the bottle due to the stiffness. Or for example, since sharper radii may not feel as comfortable during squeezing when stiffer materials are used, the designer may be misled into re-designing the bottle with greater radii. This may affect the bottle squeezability when manufactured in polyethylene or may reduce the aesthetic appeal of the bottle shape.
Other examples may be made regarding the importance of appearance of an article when made out of certain materials. For example, use of a transparent prototype composition or an overly opaque composition may mislead those viewing the article into incorrect assumptions regarding appropriate packaging, labeling, coloring, and advertising of a product.
Other considerations when trying to utilize solid imaging for prototyping include photospeed, resistance to humidity, low potential for hydrolysis, similar coefficient of friction, dimensional accuracy, ability to span without supports during fabrication, and wide process latitude.
Japanese Patent Application Hei 2-75618 describes epoxy and acrylate compositions for use in optical molding. The compositions contain at least 40 wt % of alicyclic epoxy resin with at least two epoxy groups in each molecule.
U.S. Pat. No. 5,476,784 describes cationic epoxy and acrylate compositions for use in solid imaging. The compositions may comprise from 5-40% by weight of at least one OH-terminated polyether, polyester or polyurethane. In the examples given, the polyether polyols formulations provide lower elongation at break properties that the elongation at yield properties of most low-density polyethylenes. Additionally, the patent teaches that the epoxy content is to be from 40 to 80% of the formulation by weight. Compositions made with this epoxy content are likely to produce cured articles having a higher modulus than that of polyethylene.
This invention discloses photosensitive compositions comprising;
(a) about 20-40% by weight of an epoxide-containing material;
(b) about 5-40% by weight of acrylic material selected from aromatic acrylic material, cycloaliphatic acrylic material, or combinations thereof;
(c) about 5-50% by weight of a reactive hydroxyl-containing material;
(d) at least one cationic photoinitiator; and
(e) at least one free-radical photoinitiator;
xe2x80x83with the proviso that upon exposure to actinic radiation an article is produced having the following properties:
(i) a tensile break before yield stress or a tensile yield stress greater than 13 N/mm2;
(ii) a tensile modulus in the range of about 180 to about 850 N/mm2;
(iii) a tensile break elongation before yield or a tensile yield elongation greater than 6%; and
(iv) a notched Izod :impact strength greater than 50 J/m.
The invention also relates to a process for forming a three-dimensional article, said process comprising the steps:
(1) coating a thin layer of a composition onto a surface;
(2) exposing said thin layer imagewise to actinic radiation to form an imaged cross-section, wherein the radiation is of sufficient intensity to cause substantial curing of the thin layer in the exposed areas;
(3) coating a thin layer of the composition onto the previously exposed imaged cross-section;
(4) exposing said thin layer from step (3) imagewise to actinic radiation to form an additional imaged cross-section, wherein the radiation is of sufficient intensity to cause substantial curing of the thin layer in the exposed areas and to cause adhesion to the previously exposed imaged cross-section;
(5) repeating steps (3) and (4) a sufficient number of times in order to build up the three-dimensional article;
xe2x80x83with the proviso the three-dimensional article has the following properties:
(i) a tensile break before yield stress or a tensile yield stress greater than 13 N/mm2;
(ii) a tensile modulus in the range of about 180 to about 850 N/mm2;
(iii) a tensile break elongation before yield or a tensile yield elongation greater than 6%; and
(iv) a notched Izod impact strength greater than 50 J/m.
The invention also relates to the above process wherein the composition comprises:
(a) about 20-40% by weight of an epoxide-containing material;
(b) about 5-40% by weight of an aromatic or cycloaliphatic acrylic material;
(c) about 5-50% by weight of a reactive hydroxyl-containing material;
(d) at least one cationic photoinitiator; and
(e) at least one free-radical photoinitiator.
Liquid based Solid Imaging is a process wherein a photoformable liquid is coated into a thin layer upon a surface and exposed imagewise to actinic radiation such that the liquid solidifies imagewise. Subsequently, new thin layers of photoformable liquids are coated onto previous layers of liquid or previously solidified sections. Then the new layer is exposed imagewise in order to solidify portions imagewise and in order to induce adhesion between portions of the new hardened region and portions of the previously hardened region. Each imagewise exposure is of a shape that relates to a pertinent cross-section of a photohardened object such that when all the layers have been coated and all the exposures have been completed, an integral photohardened object can be removed from the surrounding liquid composition.
One of the most important advantages of the solid imaging process is the ability to rapidly produce actual objects that have been designed by computer aided design. A significant amount of progress has been made with compositions and processes that have been adapted to improve the accuracy of the objects produced. Also, composition developers have made significant progress toward improving individual properties such as the modulus or deflection temperature of the photohardened objects. However, attempts to simulate a particular set of physical properties of a common manufacturing material to such a degree that the simulation material could be easily mistaken for the simulated material, based upon look and feel properties, have been unsuccessful.
During the development of the compositions disclosed herein, it was noted that substantial changes in the look and feel of articles fabricated by the liquid solid imaging process could be attained by slight alterations in component concentration. Surprisingly it was found that by making these alterations in composition, articles could be made that had the look and feel of articles manufactured from polyethylene materials. Within the field of liquid solid imaging such a discovery is a first in that previous commercial compositions did not make articles that elicited a similar look and feel sense with regard to any other common plastic. It was then recognized that by tailoring the composition, the properties of polyethylene manufactured articles could be simulated. This potential therefore solved an oft expressed but unfilled need to produce prototypes that not only had the appearance of desired objects but also material properties that simulated the look and feel of the materials out of which production objects were destined to be manufactured.
In order to simulate a material in terms of look and feel, it is necessary to decide upon the appropriate appearance factors and physical properties. For example, in the field of liquid solid imaging the most commonly quoted fully cured part physical properties are the tensile stress, tensile modulus, elongation at break, flexural stress, flexural modulus, impact strength, hardness, and deflection temperature. Some of these physical properties, such as for example elongation at break, are not something that can be xe2x80x9cfeltxe2x80x9d unless the material is deformed. Such physical properties are therefore not indicative of a good simulation material property.
In some cases, the characteristics of a material that serve to define the look and feel properties of a particular material are difficult to define. This is especially so in the case of how a materials looks. However, in the case of the instant invention a deliberate compositional choice was made such that articles fabricated through solid imaging means, when given various amounts of exposure to actinic radiation, had a similar color and light scattering characteristic as various grades of polyethylene. It was also found that changing the actinic exposure can also modify the feel properties of the articles manufactured from the composition by the solid imaging process. That is, when lower actinic exposures are given during the solid imaging process, the articles feel more like lower density polyethylene articles but when higher actinic exposures are given, the articles feel more like medium density polyethylene articles.
A stress-strain curve, also known as a deformation curve, shows the relationship between the stress or load on a sample and the strain or deformation that results. The tensile stress-strain curve results when the sample is under tension. The flexural stress-strain curve is a result of bending the sample. It is considered here that the tensile properties are best representative of how the articles feel.
At the beginning of stress, the stress-strain relationship is roughly linear. The xe2x80x9ctensile modulusxe2x80x9d (or the flexural modulus) is defined as the slope of the curve in this linear region. As the sample continues to be stressed, the stress-strain curve tends to become less linear until a maximum is reached. This maximum point is called the xe2x80x9cyield pointxe2x80x9d and is generally defined as the region where a large increment of extension occurs under constant load. The xe2x80x9cyield stressxe2x80x9d is the stress at the yield point. The xe2x80x9celongation at yieldxe2x80x9d is the percent elongation at the yield point. Some materials exhibit increased stress and strain capability beyond the yield point. The point at which the sample breaks is where the values of xe2x80x9cbreak stressxe2x80x9d and xe2x80x9c% elongation at breakxe2x80x9d can be ascertained. Some samples may break prior to the yield point or at the yield point. In the case of break before yield, only the break stress and % elongation at break values are reported. It is possible for the break stress to be a lower or higher value than the yield stress. All tensile properties as discussed herein were measured according to ASTM Test D-638M, except that for the example formulations and the comparative formulations the humidity was not controlled.
By far, the most important property that relates to what is felt when handling a material, is the tensile modulus. This is representative of the feeling of stiffness.
A second important property is that of the elongation of the material. When a simulation of a material is handled and flexed, it should not break or permanently distort if the material being simulated does not break or distort with such handling. With plastics there is considerable debate relating to the point at which a sample under stress transitions from an elastic mode to a plastic mode of behavior. However, most would agree that when a material begins to yield, its behavior is plastic and that any handling that brings a sample past its yield point will leave the sample permanently distorted. For the purposes of this invention the tensile elongation at yield serves to help define this aspect of the feel of a material. If a material breaks before its yield, it must have a tensile elongation at break that is greater than or equal to the tensile elongation at yield of the material being simulated or it is not an acceptable simulation material. Ideally a simulation material should have an elongation at yield that is about the same or greater than the elongation at yield of a simulated material.
A third important physical property is the tensile stress. For the purposes of this invention, a tensile stress for a material that breaks at or before its yield is an important property for simulation purposes. Simulation materials that have a yield stress or break stress (before yield) that is lower than the lowest yield stress or break stress (before yield) of a simulated material are usually unsuitable simulation materials.
Another important physical property is that of the sense of feel for inherent toughness. The Izod impact strength provides a good measure of the toughness of a material. A good simulation material will have toughness in a range that is close to that of the simulated material. For the discussion herein, the impact strength is measured by the notched Izod test, according to ASTM Test D-256A.
In general, useful articles are not really used to the point of breaking. For example, if a squeeze bottle is made of a material that breaks during normal use it will have little value. And in general, useful articles are not often used such that they are stressed past their yield capabilities. For example, if bridges were designed to withstand normal loads, such as a car, which induced stresses in support members exceeding the yield point, the bridge would increase in sag for every car that passed over it. Exceptions may be found for some applications such as, for example, living hinges. In these cases, often the first use of the article induces a stress that exceeds the yield of the material, but subsequent stresses remain for the most part within the elastic range of the material. For the purposes of the instant invention, material property values relating to the break of a material, for a material having a yield point, are of little interest in terms of simulating the look and feel of a simulated material.
The tensile stress usually quoted is the maximum tensile stress, which is either the stress at yield or the stress at break. If the material breaks before it yields, the tensile stress at break of the simulation material should be compared to the tensile yield stress of the simulated material. If the simulation material exhibits a yield point, the tensile yield stress of the simulation material should be compared to the tensile yield stress of the simulated material. In the case of low to medium density polyethylene, the tensile stress at yield is 13-28 N/mm2. Simulation materials which have a break tensile stress (before yield) or a tensile yield stress of less than 13 N/mm2, are probably not suitable as a simulation material for low to medium density polyethylene.
The tensile modulus (and/or the flexural modulus) is probably the most important physical property with respect to the feel of a material. People can generally feel the stiffness of a material and can tell if the material is not stiff enough or if the material is too stiff. This is because the modulus is a material property that is determined in the working range of a material (i.e. prior to plastic deformation of the material) and is a material property that can be felt or measured at relatively low stress levels. In general, a suitable simulation material has a tensile modulus which is within the range of moduli of the simulated material. Low density to medium density polyethylene has a tensile modulus range of from approximately 260 to 520 N/mm2. It has been found that simulation compositions resulting in parts having a tensile modulus in the range of about 180 to about 850 N/mm2 are suitable simulation materials. Parts having a modulus below that range are generally too soft and pliable to have any utility as a polyethylene simulation. Conversely, parts having a modulus above that range are too stiff. Preferably, the compositions result in parts having a tensile modulus in the range of about 220 to about 650 N/mm2.
In the case of the most preferred simulation material for polyethylene, it has been discovered that variations in the exposure during the solid imaging process lead to significant variations in the tensile modulus. For example, by doubling the exposure of this material during the solid imaging process the tensile modulus doubled but the elongation at yield remained unchanged. This is extremely advantageous for a simulation material since the modulus can be varied over a range that very closely matches the modulus range of the simulated material. Such a simulation material is therefore adaptable to simulate various molecular weights and grades of polyethylene, for example.
The elongation properties of a simulation material are also important. If the simulation material has a tensile elongation at break that is lower than the minimum tensile elongation at yield of the simulated material, it is regarded as not suitable. If the material has a yield point, the tensile elongation at yield of the simulation material is compared with the tensile elongation at yield of the simulated material. If the material does not have a yield point, the tensile elongation at break of the simulation material is compared with the tensile elongation at yield of the simulated material. Suitable simulation materials have tensile elongation at yield or tensile elongation at break (before yield) values that equal or exceed the tensile elongation at yield values of the simulation material. Low to medium density polyethylene has a tensile elongation at yield range of 6-8%. Therefore a suitable simulation material for polyethylene will have a tensile elongation at break (before yield) or a tensile elongation at yield of greater than 6%.
The impact resistance of a simulation material relative to the impact resistance of a simulated material is also of some importance. For example, it is not unusual for someone handling an object to knock the object against the corner of a table. From such treatment a feel of the materials toughness and sound qualities (deadening, ringing, etc.) can be garnered. For the purposes of this patent, a suitable simulation material will have an Izod impact strength that is nearly as strong as the Izod impact strength of the simulation material. Low to medium density polyethylene has a notched Izod Impact Strength of 53.4 J/m to No Break. Therefore a suitable simulation material for low to medium density polyethylene has Notched Izod Impact Strength of at least 50 J/m.
The appearance of a simulation material is also an important consideration. Low to medium density polyethylene has a cloudy appearance. Therefore a suitable simulation material for low to medium density polyethylene should also have a cloudy appearance and as much as possible for UV cured materials, minimum color.
The compositions of the invention generally comprise an epoxide-containing material, a free-radical polymerizable aromatic and/or cycloaliphatic acrylic material, a reactive hydroxyl-containing material, a cationic photoinitiator and a free-radical photoinitiator.
The epoxide-containing materials that are used in the compositions, according to this invention, are compounds that possess on average at least one 1,2-epoxide group in the molecule. By xe2x80x9cepoxidexe2x80x9d is meant the three-membered ring
The epoxide-containing materials, also referred to as epoxy materials, are cationically curable, by which is meant that polymerization and/or crosslinking and other reaction of the epoxy group is initiated by cations. The materials can be monomers, oligomers or polymers and are sometimes referred to as xe2x80x9cresins.xe2x80x9d Such materials may have an aliphatic, aromatic, cycloaliphatic, araliphatic or heterocyclic structure; they comprise epoxide groups as side groups, or those groups form part of an alicyclic or heterocyclic ring system. Epoxy resins of those types are generally known and are commercially available.
The epoxide-containing material (a) may be a solid or a liquid which is soluble or dispersible in the remaining components. It is preferred that the epoxide-containing material comprise at least one liquid component such that the combination of materials is a liquid. In the preferred case, the epoxide-containing material can be a single liquid epoxy material, a combination of liquid epoxy materials, or a combination of liquid epoxy material(s) and solid epoxy material(s) which is soluble in the liquid.
Examples of suitable epoxy materials include polyglycidyl and poly(-methylglycidyl) esters of polycarboxylic acids. The polycarboxylic acid can be aliphatic, such as, for example, glutaric acid, adipic acid and the like; cycloaliphatic, such as, for example, tetrahydrophthalic acid; or aromatic, such as, for example, phthalic acid, isophthalic acid, trimellitic acid, or pyromellitic acid. It is likewise possible to use carboxy-terminated adducts, for example, of trimellitic acid and polyols, such as, for example, glycerol or 2,2-bis(4-hydroxycyclohexyl)propane.
Suitable epoxy materials also include polyglycidyl or poly(-methylglycidyl) ethers obtainable by the reaction of a compound having at least two free alcoholic hydroxy groups and/or phenolic hydroxy groups and a suitably substituted epichlorohydrin. The alcohols can be acyclic alcohols, such as, for example, ethylene glycol, diethylene glycol, and higher poly(oxyethylene) glycols; cycloaliphatic, such as, for example, 1,3- or 1,4-dihydroxycyclohexane, bis(4-hydroxycyclohexyl)methane, 2,2-bis(4-hydroxycyclohexyl)propane, or 1,1-bis(hydroxymethyl)cyclohex-3-ene; or contain aromatic nuclei, such as N,N-bis(2-hydroxyethyl)aniline or p,pxe2x80x2-bis(2-hydroxyethylamino)diphenylmethane.
The epoxy compounds may also be derived from mono nuclear phenols, such as, for example, from resorcinol or hydroquinone, or they are based on polynuclear phenols, such as, for example, bis(4-hydroxyphenyl)methane (bisphenol F), 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), or on condensation products, obtained under acidic conditions, of phenols or cresols with formaldehyde, such as phenol novolacs and cresol novolacs.
Suitable epoxy materials also include poly(N-glycidyl) compounds are, for example, obtainable by dehydrochlorination of the reaction products of epichlorohydrin with amines that comprise at least two amine hydrogen atoms, such as, for example, n-butylamine, aniline, toluidine, m-xylylene diamine, bis(4-aminophenyl)methane or bis(4-methylaminophenyl)methane. The poly(N-glycidyl) compounds also include, however, N,Nxe2x80x2-diglycidyl derivatives of cycloalkyleneureas, such as ethyleneurea or 1,3-propyleneurea, and N,Nxe2x80x2-diglycidyl derivatives of hydantoins, such as of 5,5-dimethylhydantoin.
Examples of suitable epoxy materials include poly(S-glycidyl) compounds which are di-S-glycidyl derivatives which are derived from dithiols, such as, for example, ethane-1,2-dithiol or bis(4-mercaptomethylphenyl) ether.
Examples of suitable epoxy materials include epoxy compounds in which the epoxy groups form part of an alicyclic or heterocyclic ring system are bis(2,3-epoxycyclopentyl)ether, 2,3-epoxy cyclopentyl glycidyl ether, 1,2-bis(2,3-epoxycyclopentyloxy)ethane, bis(4-hydroxycyclohexyl)methane diglycidyl ether, 2,2-bis(4-hydroxycyclohexyl)propane diglycidyl ether, 3,4-epoxycyclo-hexylmethyl-3,4-epoxycyclohexane, 3,4-epoxy-6-methyl-cyclohexyl-methyl-3,4-epoxy-6-methylcyclohexanecaboxylate, di-(3,4-epoxycyclohexylmethyl)hexanedioate, di-(3,4-epoxy-6-methyl-cyclohexylmethyl)hexanedioate, ethylenebis(3,4-epoxycyclohexanecarboxylate), ethanedioldi-(3,4-epoxycyclohexylmethyl)ether, vinylcyclohexene dioxide, dicyclopentadiene diepoxide, or 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-1,3-dioxane.
It is, however, also possible to use epoxy resins in which the 1,2-epoxy groups are bonded to different hetero atoms or functional groups. Those compounds include, for example, the N,N,O-triglycidyl derivative of 4-aminophenol, the glycidyl ether glycidyl ester of salicylic acid, N-glycidyl-Nxe2x80x2-(2-glycidyloxypropyl)-5,5-dimethylhydantoin, or 2-glycidyloxy-1,3-bis(5,5-dimethyl-1-glycidylhydantoin-3-yl)propane.
In addition, liquid pre-reacted adducts of such epoxy resins with hardeners are suitable for epoxy resins.
It is of course also possible to use mixtures of epoxy materials in the compositions according to the invention.
Preferred epoxy materials are cycloaliphatic diepoxides. Especially preferred are bis(4-hydroxycyclohexyl)methane diglycidyl ether, 2,2-bis(4-hydroxycyclohexyl)propane diglycidyl ether, 3,4-epoxycyclohexylmethyl-3,4 epoxycyclohexanecarboxylate, 3,4-epoxy-6-methyl-cyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate, di-(3,4-epoxycyclohexylmethyl)hexanedioate, di-(3,4-epoxy-6-methyl-cyclohexylmethyl)hexanedioate, ethylenebis(3,4-epoxycyclohexanecarboxylate), ethanediol-di-(3,4-epoxycyclohexylmethyl) ether, and 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-1,3-dioxane.
The epoxy materials can have molecular weights which vary over a wide range. In general, the epoxy equivalent weight, i.e., the number average molecular weight divided by the number of reactive epoxy groups, is preferably in the range of about 60 to about 1000.
The free-radical polymerizable acrylic materials that are used in the composition, according to this invention, are compounds that have, on average, at least one acrylic group which can be either the free acid or an ester. By xe2x80x9cacrylicxe2x80x9d is meant the group CH2xe2x95x90CR1xe2x80x94CO2xe2x80x94, where R1 can be hydrogen or methyl. By xe2x80x9c(meth)acrylatexe2x80x9d is meant an acrylate, methacrylate or combinations thereof. The acrylic materials undergo polymerization and/or crosslinking reactions initiated by free radicals. The acrylic materials can be monomers, oligomers or polymers. It is preferred that the acrylic material be a monomer or oligomer.
Suitable as the acrylic component are, for example, the diacrylates of cycloaliphatic or aromatic diols, such as 1,4-dihydroxymethylcyclohexane, 2,2-bis(4-hydroxycycyclohexyl)propane, bis(4hydroxycyclohexyl)methane, hydroquinone, 4,4-dihydroxybiphenyl, bisphenol A, bisphenol F, bisphenol S, ethoxylated or propoxylated bisphenol A, ethoxylated or propoxylated bisphenol F, or ethoxylated or propoxylated bisphenol S. Such acrylates are known and some of them are commercially available.
Preferred are compositions comprising as the acrylic component a compound of formula I, II, III or IV
wherein
Y is a direct bond, C1-C6 alkylene, xe2x80x94Sxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94SOxe2x80x94, xe2x80x94SO2xe2x80x94, or xe2x80x94COxe2x80x94, R10 is a C1-C8 alkyl group, a phenyl group that is unsubstituted or substituted by one or more C1-C4 alkyl groups, hydroxy groups or halogen atoms, or a radical of the formula CH2-R11, wherein R11 is a C1-C8 alkyl group or a phenyl group, and A is a radical of the formula
or comprising as the acrylic component a compound of any one of formulae Va to Vd,
and the corresponding isomers,
If a substituent is C1-C4 alkyl or C1-C8 alkyl, it may be straight-chained or branched. A C1-C4 alkyl may be, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl or tert-butyl, and a C1-C8 alkyl may additionally be, for example, the various pentyl, hexyl, heptyl, or octyl isomers.
If a substituent is halogen, it is fluorine, chlorine, bromine, or iodine, but especially chlorine or bromine.
If a substituent is C1-C6 alkylene it is, for example, methylene, ethylene, propylene (methylethylene), trimethylene, 1,1-propanediyl, 2,2-propanediyl, tetramethylene, ethylmethylene, 1,1-butanediyl, 2,2-butanediyl, pentamethylene or hexamethylene. The alkylene radicals may also be substituted by halogen atoms. Examples of halogenated alkylene radicals are xe2x80x94C(CCl3)2xe2x80x94 and xe2x80x94C(CF3)2xe2x80x94.
Especially preferred in the compositions are compounds of the formula V, VI or VII wherein Y is xe2x80x94CH2xe2x80x94 or xe2x80x94(CH3)2xe2x80x94. Also especially preferred are compounds of formula VII wherein R10 is n-butyl, phenyl, n-butoxymethyl, or phenoxymethyl.
Suitable as aromatic tri(meth-)acrylates are, for example, the reaction products of triglycidyl ethers of trihydric phenols, and phenol or cresol novolacs having three hydroxy groups with (meth)-acrylic acid.
Compositions wherein the acrylic component is an acrylate of bisphenol A diepoxide such as Ebecryl(copyright) 3700 from UCB Chemical Corporation, Smyrna, Ga. or an acrylate of 1,4-cyclohexanedimethanol are especially preferred for compositions used in this invention.
In addition to the aromatic or cycloaliphatic acrylic material (b), other acrylic materials can be present. Liquid poly(meth-)acrylates having functionality of greater than 2 which may, where appropriate, be used in the compositions according to the invention. These can be, for example, tri-, tetra-, or penta-functional monomeric or oligomeric aliphatic, (meth)acrylates.
Suitable as aliphatic polyfunctional (meth)acrylates are, for example, the triacrylates and trimethacrylates of hexane-2,4,6-triol, glycerol, or 1,1,1-trimethylolpropane, ethoxylated or propoxylated glycerol, or 1,1,1-trimethylolpropane and the hydroxy group-containing tri(meth)acrylates which are obtained by the reaction of triepoxy compounds, such as, for example, the triglycidyl ethers of the mentioned triols, with (meth)acrylic acid. It is also possible to use, for example, pentaerythritol tetra-acrylate, bistrimethylolpropane tetra-acrylate, pentaerythritol monohydroxytri(meth)acrylate, or dipentaerythritol monohydroxypehta(meth)acrylate.
It is also possible to use hexafunctional urethane (meth)acrylates. Those urethane (meth)acrylates are known to the person skilled in the art and can be prepared in known manner, for example by reacting a hydroxy-terminated polyurethane with acrylic acid or methacrylic acid, or by reacting an isocyanate-terminated prepolymer with hydroxyalkyl (meth)acrylates to follow the urethane (meth)acrylate. Also useful are (meth)acrylates such as tris(2-hydroxyethyl)isocyanurate triacrylate.
The reactive hydroxyl-containing material which is used in the present invention may be any organic material having hydroxyl functionality of at least 1, and preferably at least 2. The material may be a liquid or a solid that is soluble or dispersible in the remaining components. The material should be substantially free of any groups which inhibit the curing reactions, or which are thermally or photolytically unstable.
Preferably the organic material contains two or more primary or secondary aliphatic hydroxyl groups, by which is meant that the hydroxyl group is bonded directly to a non-aromatic carbon atom. The hydroxyl group may be internal in the molecule or terminal. Monomers, oligomers or polymers can be used. The hydroxyl equivalent weight, i.e., the number average molecular weight divided by the number of hydroxyl groups, is preferably in the range of about 31 to 5000.
Representative examples of suitable organic materials having a hydroxyl functionality of 1 include alkanols, monoalkyl ethers of polyoxyalkyleneglycols, monoalkyl ethers of alkylene-glycols, and others.
Representative examples of useful monomeric polyhydroxy organic materials include alkylene and arylalkylene glycols and polyols, such as 1,2,4-butanetriol, 1,2,6-hexanetriol, 1,2,3-heptanetriol, 2,6-dimethyl-1,2,6-hexanetriol, (2R,3R)-(xe2x88x92)-2-benzyloxy-1,3,4-butanetriol, 1,2,3-hexanetriol, 1,2,3-butanetriol, 3-methyl-1,3,5-pentanetriol, 1,2,3-cyclohexanetriol, 1,3,5-cyclohexanetriol, 3,7,11,15-tetramethyl-1,2,3-hexadecanetriol, 2-hydroxymethyl-tetrahydro-pyran-3,4,5-triol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, 1,3-cyclopentanediol, trans-1,2-cyclooctanediol, 1,16-hexadecanediol, 3,6-dithia-1,8-octanediol, 2-butyne-1,4-diol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1-phenyl-1,2-ethanediol, 1,2-cyclohexanediol, 1,5-decalindiol, 2,5-dimethyl-3-hexyne-2,5-diol, 2,7-dimethyl-3,5-octadiyne-2-7-diol, 2,3-butanediol, 1,4-cyclohexanedimethanol.
Representative examples of useful oligomeric and polymeric hydroxyl-containing materials include polyoxyethylene and polyoxypropylene glycols and triols of molecular weights from about 200 to about 10,000; polytetramethylene glycols of varying molecular weight; copolymers containing pendant hydroxy groups formed by hydrolysis or partial hydrolysis of vinyl acetate copolymers, polyvinylacetal resins containing pendant hydroxyl groups; hydroxy-terminated polyesters and hydroxy-terminated polylactones; hydroxy-functionalized polyalkadienes, such as polybutadiene; and hydroxy-terminated polyethers.
Preferred hydroxyl-containing monomers are 1,4-cyclohexanedimethanol and aliphatic and cycloaliphatic mono-hydroxy alkanols.
Preferred hydroxyl-containing oligomers and polymers include hydroxyl and hydroxyl/epoxy functionalized polybutadiene, polycaprolactone diols and triols, ethylene/butylene polyols, and combinations thereof. Preferred examples of polyether polyols are polypropylene glycols of various molecular weights and glycerol propoxylate-B-ethoxylate triol. Especially preferred are linear and branched polytetrahydrofuran polyether polyols available in various molecular weights, such as for example 250, 650, 1000, 2000, and 2900 MW.
In the compositions according to the invention, any type of photoinitiator that, upon exposure to actinic radiation, forms cations that initiate the reactions of the epoxy material(s) can be used. There are a large number of known and technically proven cationic photoinitiators for epoxy resins that are suitable. They include, for example, onium salts with anions of weak nucleophilicity. Examples are halonium salts, iodosyl salts or sulfonium salts, such as are described in published European patent application EP 153904, sulfoxonium salts, such as described, for example, in published European patent applications EP 35969, 44274, 54509, and 164314, or diazonium salts, such as described, for example, in U.S. Pat. Nos. 3,708,296 and 5,002,856. Other cationic photoinitiators are metallocene salts, such as described, for example, in published European applications EP 94914 and 94915.
A survey of other current onium salt initiators and/or metallocene salts can be found in xe2x80x9cUV-Curing, Science and Technologyxe2x80x9d, (Editor S. P. Pappas, Technology Marketing Corp., 642 Westover Road, Stanford, Conn., U.S.A.) or xe2x80x9cChemistry and Technology of UV and EB Formulation for Coatings, Inks and Paintsxe2x80x9d, Vol. 3 (edited by P. K. T. Oldring).
Preferred cationic photoinitiators are compounds of formula VI, VII, or VIII below,
[R1xe2x80x94Ixe2x80x94R2]+[Qm]xe2x88x92xe2x80x83xe2x80x83(VI)

wherein:
R1, R2, R3, R4, R5, R6, and R7 are each independently of the others C6-C18 aryl that is unsubstituted or substituted by suitable radicals,
L is boron, phosphorus, arsenic, or antimony,
Q is a halogen atom or some of the radicals Q in an anion
LQmxe2x88x92 may also be hydroxy groups, and
m is an integer that corresponds to the valence of L plus 1.
Examples of C6-C18 aryl are phenyl, naphthyl, anthryl, and phenanthryl. Any substituents present for suitable radicals are alkyl, preferably C1-C6 alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, or the various pentyl or hexyl isomers, alkoxy, preferably C1-C6 alkoxy such as methoxy, ethoxy, propoxy, butoxy, pentyloxy, or hexyloxy, alkylthio, preferably C1-C6 alkylthio, such as methylthio, ethylthio, propylthio, butylthio, pentylthio, or hexylthio, halogen, such as fluorine, chlorine, bromine, or iodine, amino groups, cyano groups, nitro groups, or arylthio, such as phenylthio.
Examples of preferred halogen atoms Q are chlorine and especially fluorine. Preferred anions LQmxe2x88x92 are BF4xe2x88x92, PF6xe2x88x92, AsF6xe2x88x92, SbF6xe2x88x92, and SbF5(OH)xe2x88x92.
Especially preferred are compositions comprising as the cationic photoinitiator a compound of formula VIII wherein R5, R6 and R7 are aryl, aryl being especially phenyl or biphenyl, or mixtures of those two compounds.
Also preferred are compositions comprising as the cationic photoinitiator component compounds of formula (IX)
[R8(FeIIR9)c]d+c[x]cxe2x88x92d,xe2x80x83xe2x80x83
wherein,
c is 1 or 2,
d is 1,2,3,4 or 5,
X is a non-nucleophilic anion, especially PF6xe2x88x92, AsF6xe2x88x92, SbF6xe2x88x92, CF3SO3xe2x88x92, C2F5SO3xe2x88x92, n-C3F7SO3xe2x88x92, n-C4F9SO3xe2x88x92, n-C6F13SO3xe2x88x92, or n-C8F17SO3xe2x88x92, R8 is a pi-arene, and R9 is an anion of a pi-arene, especially a cyclopentadienyl anion.
Examples of pi-arenes as R8 and anions of pi-arenes as R9 are to be found in published European patent application EP 94915.
Examples of preferred pi-arenes as R8 are toluene, xylene, ethylbenzene, cumene, methoxybenzene, methylnaphthalene, pyrene, perylene, stilbene, diphenylene oxide and diphenylene sulfide. Especially preferred are cumene, methylnaphthalene, or stilbene.
Examples of non-nucleophilic anions Xxe2x88x92 are FSO3xe2x88x92, anions of organic sulfonic acids, of carboxylic acids, or anions LQmxe2x88x92, as already defined above.
Preferred anions are derived from partially fluoro- or perfluoro-aliphatic or partially fluoro- or perfluoro-aromatic carboxylic acids, or especially from partially fluoro- or per-fluoro-aliphatic or partially fluoro or perfluoro-aromatic organic sulfonic acids, or they are preferably anions LQmxe2x88x92.
Examples of anions X are BF4xe2x88x92, PF6xe2x88x92, AsF6xe2x88x92, SbF6xe2x88x92, SbF5(OH)xe2x88x92, CF3SO3xe2x88x92, C2F5SO3xe2x88x92, n-C3F7SO3xe2x88x92, n-C4F9SO3xe2x88x92, n-C6F13SO3xe2x88x92, n-C8F17SO3xe2x88x92, C6F5SO3xe2x88x92, phosphorus tungstate, or silicon tungstate. Preferred are PF6xe2x88x92, AsF6xe2x88x92, SbF6xe2x88x92, CF3SOxe2x88x92, C2F5SO3xe2x88x92, n-C3F7SO3xe2x88x92, n-C4F9SO3xe2x88x92, n-C6F13SO3xe2x88x92, and n-C8F17SO3xe2x88x92.
The metallocene salts can also be used in combination with oxidizing agents. Such combinations are described in published European patent application EP 126712.
In order to increase the light efficiency, or to sensitize the cationic photoinitiator to specific wavelengths, such as for example specific laser wavelengths or a specific series of laser wavelengths, it is also possible, depending on the type of initiator, to use sensitizers. Examples are polycyclic aromatic hydrocarbons or aromatic keto compounds. Specific examples of preferred sensitizers are mentioned in published European patent application EP 153904. Other preferred sensitizers are benzo[g,h,i]perylene, 1,8-diphenyl-1,3,5,7-octatetraene, and 1,6-diphenyl-1,3,5-hexatriene as described in U.S. Pat. No. 5,667,937. It will be recognized that an additional factor in the choice of sensitizer is the nature and primary wavelength of the source of actinic radiation.
In the compositions according to the invention, any type of photoinitiator that forms free radicals when the appropriate irradiation takes place can be used. Typical compounds of known photoinitiators are benzoins, such as benzoin, benzoin ethers, such as benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether, benzoin phenyl ether, and benzoin acetate, acetophenones, such as acetophenone, 2,2-dimethoxyacetophenone, 4-(phenylthio)acetophenone, and 1,1-dichloroacetophenone, benzil, benzil ketals, such as benzil dimethyl ketal, and benzil diethyl ketal, anthraquinones, such as 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 1-chloroanthraquinone, and 2-amylanthraquinone, also triphenylphosphine, benzoylphosphine oxides, such as, for example, 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Lucirin(copyright) TPO), benzophenones, such as benzophenone, and 4,4xe2x80x2-bis(N,Nxe2x80x2-dimethylamino)benzophenone, thioxanthones and xanthones, acridine derivatives, phenazene derivatives, quinoxaline derivatives or 1-phenyl-1,2-propanedione-2-O-benzoyloxime, 1-aminophenyl ketones or 1-hydroxyphenyl ketones, such as 1-hydroxycyclohexyl phenyl ketone, phenyl (1-hydroxyisopropyl)ketone and 4-isopropylphenyl(1-hydroxyisopropyl)ketone, or triazine compounds, for example, 4xe2x80x3xe2x80x2methyl thiophenyl-1-di(trichloromethyl)-3,5 S-triazine, S-triazine-2-(stylbene)-4,6-bis-trichloromethyl, and paramethoxy stiryl triazine, all of which are known compounds.
Especially suitable free-radical photoinitiators, which are normally used in combination with a He/Cd laser, operating at for example 325 nm, an Argon-ion laser, operating at for example 351 nm, or 351 and 364 nm, or 333, 351, and 364 nm, or a frequency tripled YAG-solid state laser, having an output of 351 or 355 nm, as the radiation source, are acetophenones, such as 2,2-dialkoxybenzophenones and 1-hydroxyphenyl ketones, for example 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-1-(4-(2-hydroxyethoxy)phenyl)-2-methyl-1-propanone, or 2-hydroxyisopropyl phenyl ketone (also called 2-hydroxy-2,2-dimethylacetophenone), but especially 1-hydroxycyclohexyl phenyl ketone. Another class of free-radical photoinitiators comprises the benzil ketals, such as, for example, benzil dimethyl ketal. Especially an alpha-hydroxyphenyl ketone, benzil dimethyl ketal, or 2,4,6-trimethylbenzoyldiphenylphosphine oxide is used as photoinitiator.
Another class of suitable free radical photoinitiators comprises the ionic dye-counter ion compounds, which are capable of absorbing actinic rays and producing free radicals, which can initiate the polymerization of the acrylates. The compositions according to the invention that comprise ionic dye-counter ion: compounds can thus be cured in a more variable manner using visible light in an adjustable wavelength range of 400 to 700 nanometers. Ionic dye-counter ion compounds and their mode of action are known, for example from published European patent application EP 223587 and U.S. Pat. Nos. 4,751,102, 4,772,530 and 4,772,541. There may be mentioned as examples of suitable ionic dye-counter ion compounds the anionic dye-iodonium ion complexes, the anionic dye-pyryllium ion complexes and, especially, the cationic dye-borate anion compounds of the following formula
wherein D+ is a cationic dye and R12, R13, R14, and R15 are each independently of the others arkyl, aryl, alkaryl, allyl, aralkyl, alkenyl, alkynyl, an alicyclic or saturated or unsaturated heterocyclic group. Preferred definitions for the radicals R12 to R15 can be found, for example, in published European patent application EP 223587.
Especially preferred is the free-radical photoinitiator 1-hydroxyphenyl ketone, which produces parts having the least amount of yellowing after final cure and provides articles which most closely simulate polyethylene.
Other additives which are known to be useful in solid imaging compositions may also be present in the composition of the invention. Stabilizers are often added to the compositions in order to prevent a viscosity build-up during usage in the solid imaging process. The preferred stabilizers are described in U.S. Pat. No. 5,665,792. Such stabilizers are usually hydrocarbon carboxylic acid salts of group IA and IIA metals. Most preferred examples of these salts are sodium bicarbonate, potassium bicarbonate, and rubidium carbonate. Rubidium carbonate is preferred for formulations of this invention with recommended amounts varying between 0.0015 to 0.005% by weight of composition. Alternative stabilizers are polyvinylpyrrolidones and polyacrylonitriles. Other possible additives include dyes, pigments, fillers, wetting agents, photosensitizers for the free-radical photoinitiator, leveling agents, surfactants and the like.
The compositions of the invention generally comprise from about 20% by weight to less than about 40% by weight of the epoxide-containing material, based on the total weight of the composition.
It is sometimes beneficial to describe the compositions in terms of equivalents or milliequivalents of epoxy material per 100 grams of total composition. The epoxy equivalent weight can be derived by dividing the number of epoxy groups contained within a molecule by the molecular weight of the molecule. The total epoxy equivalent weight of a composition is determined by first calculating the epoxy content of each component, i.e., epoxide-containing material, epoxy-acrylate, etc. The individual component epoxy equivalent weights are weight averaged for the entire composition. It is preferred that the compositions comprise from about 250 to about 350 milliequivalents of epoxy per 100 grams of composition.
The compositions of the invention preferably comprise from about 5% to about 45% by weight of free-radical polymerizable acrylic material, based on the total weight of the composition. It is most preferred that the acrylic be an aromatic and/or cycloaliphatic diacrylate or di-methacrylate.
The compositions of the invention preferably comprise from about 5% to about 50% by weight of reactive hydroxy-containing material, based on the total weight of the composition, more preferably from about 20% to about 30% by weight.
It is sometimes beneficial to describe the compositions in terms of equivalents or milliequivalents of hydroxyl-containing material per 100 grams of total composition. The hydroxyl equivalent weight can be derived by dividing the number of hydroxyl groups contained within a molecule by the molecular weight of the molecule. The total number of equivalent of equivalent of hydroxyl in a composition is determined by first calculating the hydroxyl content of each component, i.e., epoxide-containing material, epoxy-acrylate, polyol, initiator, etc. The individual component hydroxyl equivalent weights are weight averaged for the entire composition. All hydroxyls are assumed to be reactive, regardless of steric hindrance. It is preferred that the compositions comprise from about 140 to about 180 milliequivalents of reactive hydroxy-containing material per 100 grams of composition. It is most preferred that the ratio of epoxy equivalents to hydroxyl equivalents be in the range from about 1.5 to about than 2.5; most preferably 1.9 to 2.4.
The compositions of the invention preferably comprise from about 0.2 to about 10% by weight of cationic photoinitiator, based on the total weight of the composition.
The compositions of the invention preferably comprise from about 0.01 to about 10% by weight of free-radical photoinitiator, based on the total weight of the composition.
The compositions of the invention can be prepared according to conventional procedures. In general, the components are combined by mixing in any suitable mixing apparatus. In some cases, some components can be premixed before adding to the total composition. In some cases, the mixing is carried out in the absence of light. In some cases, the mixing is carried out with some heating, generally at temperatures that range from about 30xc2x0 C. to about 60xc2x0 C.
The process for producing three-dimensional articles from the compositions of the invention, as discussed above, generally involves exposure of successive thin layers of the liquid composition to actinic radiation. A thin layer of the photosensitive composition of the invention is coated onto a surface. This is most conveniently done if the composition is a liquid. However, a solid composition can be melted to form a layer. The thin layer is then exposed imagewise to actinic radiation. The radiation must provide sufficient exposure to cause substantial curing of the photosensitive composition in the exposed areas. By xe2x80x9csubstantial curingxe2x80x9d it is meant that the photosensitive composition has reacted to an extent such that the exposed areas are physically differentiable from the unexposed areas. For liquid, gel or semi-solid photosensitive compositions, the cured areas will have hardened or solidified to a non-fluid form. For solid photosensitive compositions, the exposed areas will have a higher melting point than the non-exposed areas. Preferably, the exposure is such that portions of each successive layer are adhered to a portion of a previously exposed layer or support region, or to portions of a platform surface. This first exposure step forms a first imaged cross-section. An additional (second) thin layer of photosensitive composition is then coated onto the first imaged cross-section and imagewise exposed to actinic radiation to form an additional (second) imaged cross-section. These steps are repeated with the fifth thin layer of photosensitive composition being coated onto the xe2x80x9c(nxe2x88x921)thxe2x80x9d imaged cross-section and exposing to actinic radiation. The repetitions are carried out a sufficient number of times to build up the entire three-dimensional article.
The radiation is preferably in the range of 280-650 nm. Any convenient source of actinic radiation can be used, but lasers are particularly suitable. Useful lasers include HeCd, argon, nitrogen, metal vapor, and NdYAG lasers. The exposure energy is preferably in the range of about 10-75 mJ/cm2. Suitable methods and apparatus for carrying out the exposure and production of three-dimensional articles have been described in, for example, U.S. Pat. Nos. 4,987,044, 5,014,207, and 5,474,719, which teaches the use of pseudoplastic, plastic flow, thixotropic, gel, semi-solid and solid photopolymer materials in the solid imaging process.
In general, the three-dimensional article formed by exposure to actinic radiation, as discussed above, is not fully cured, by which is meant that not all of the reactive material in the composition has reacted. Therefore, there is often an additional step of more fully curing the article. This can be accomplished by further irradiating with actinic radiation, heating, or both. Exposure to actinic radiation can be accomplished with any convenient radiation source, generally a UV light, for a time ranging from about 10 to over 60 minutes. Heating is generally carried out at a temperature in the range of about 75-150xc2x0 C., for a time ranging from about 10 to over 60 minutes.

Solid imaging compositions for preparing polyethylene-like articles


Propylene polymer composites containing modified clays and compatibilizing agents, more specifically hydrogenated tallow modified montmorillonite and maleic anhydride grafted propylene polymers, are provided. Concentrates or masterbatches used to prepare the composites are also described. The improved composites of the invention exhibit increased melt strength compared to the base resin and to composites similarly formulated using other types of modified clays. Moreover, the improved results are achievable at lower compatibilizer levels and lower ratios of compatibilizer to clay than has heretofore been considered practical.

1. Field of the Invention
The invention relates to improved propylene polymer composites and to masterbatch compositions utilized for their preparation. Propylene polymer composites produced in accordance with the invention having increased melt strength and other improved physical properties contain a clay modified with a hydrogenated tallow quaternary ammonium compound and a propylene polymer compatibilizing agent.
2. Description of the Prior Art
Propylene polymer resins have enjoyed significant growth in recent years in view of the diverse resin types which are available. In addition to propylene homopolymer, numerous copolymers of propylene with ethylene and other xcex1-olefins are now commercially produced. These include random copolymers, block copolymers and multi-phase polymer systems. This latter group of resins includes the so-called impact copolymers and thermoplastic elastomers (TPEs) which consist of a continuous phase of a crystalline polymer, e.g., highly isotactic propylene homopolymer, having a rubbery phase, e.g., ethylene-propylene copolymer, dispersed therein.
These resins are widely used in extrusion for the production of films, fibers and wide variety of molded goods, such as bottles, hose and tubing, auto parts and the like. While it is necessary that these resins have sufficiently low melt viscosity under conditions of high shear encountered in the extruder, in order to have acceptable processability and achieve the high throughputs necessary for commercial operations, the resin must also have sufficient melt strength after extrusion to prevent sagging/distortion of the extrudate before it is cooled below the melt point. High melt strength resins are particularly advantageous for the production of large thermoformed and blow molded articles, for extrusion coating and for foamed and sheet extrusions. For example, a blow molding resin suitable for the production of small shampoo bottles may not have sufficient melt strength for the production of one-gallon jugs where the parison is substantially larger and heavier.
The goal of the present invention is to provide propylene polymer composites which exhibit increased melt strength. It is a further objective to accomplish this through the use of a quaternary ammoniumxe2x80x94modified clays, thereby achieving the enhanced physical and mechanical properties typically associated with these filled systems.
The use of organically modified clays, sometimes referred to as intercalates or organoclays, produced by a cation exchange reaction between the silicate and alkylammonium salts, especially quaternary ammonium compounds is known in the prior art. The alkyl cations exchanged into and between the clay platelets increase interlayer spacing between adjacent platelets and render the hydrophilic clay organophilic and thus more easily dispersed in thermoplastic resins. Compared to conventional filled thermoplastic compositions, thermoplastics filled with the intercalated organoclays have improved physical properties at similar loading levels.
With polymers which are nonpolar or have low polarity, such as polypropylene, it is generally considered to be necessary to include a compatibilizer resin for effective intercalation. The compatibilizers are most commonly maleic anhydride grafted polypropylene and are employed at a weight ratio of 3:1 (compatibilizer:organoclay). While propylene polymer composites have been prepared using ratios of compatibilizer to organoclay as low as 1:1, these lower ratios are generally considered to be less desirable and, therefore, typically avoided. Hasegawa, et al., in their article entitled xe2x80x9cPreparation and Mechanical Properties of Polypropylene-Clay Hybrids Using a Maleic Anhydride Modified Polypropylene Oligomer,xe2x80x9d JAPS 67, 87 (1998), observed that the particles of the silicate layers became smaller and were dispersed more uniformly as the ratio of the maleic anhydride grafted polypropylene compatibilizer was increased. They further concluded that as the dispersability of the clays was improved, the reinforcement effect of the clays increased.
We have now discovered that by utilizing certain organoclay/compatibilizer combinations, it is possible to significantly improve the melt strength of propylene polymer composites. Furthermore, this improvement is unexpectedly obtained at lower compatibilizer levels and lower ratios of compatibilizer to modified clay than was heretofore considered possible by the prior art.
The present invention relates to propylene polymer composites having improved melt strength. More specifically, the compositions of the invention comprise a thermoplastic resin composite having improved melt strength comprising: 76 to 99 weight percent, based on the total composition, of a thermoplastic propylene homopolymer, copolymer or blends thereof, 0.5 to 12 weight percent of an organically modified clay consisting of a smectite clay that has been ion-exchanged and intercalated with a quaternary ammonium compound of the formula:
(R)n(CH3)mN+Clxe2x88x92
where R represents a hydrogenated tallow moiety, n is 1 to 4, m is 0 to 3 and n+m=4; and 0.5 to 12 weight percent of a propylene polymer compatibilizing agent obtained by copolymerizing or grafting 0.1 to 8 weight percent ethylenically unsaturated carboxylic acid or derivative monomer with propylene. The weight ratio of organically modified clay to compatibilizer will range from 1:5 to 1:0.1.
In a preferred embodiment of the invention the organically modified clay is a montmorillonite clay modified with dimethyl dihydrogenated tallow ammonium chloride and the compatibilizing agent is a propylene homopolymer or copolymer of propylene or ethylene grafted with 0.2 to 2.5 weight percent maleic anhydride. It is especially useful if the modified clay has a modifier concentration of 95 to 140 meq/100 g and the compatibilizing agent has a melt flow from 40 to 400 g/10 min. Preferred composites contain 84 to 98.75 weight percent base resin, 1 to 8 weight percent modified clay and 1 to 8 weight percent comptabilizing agent with the modified clay and compatibilizer present at a weight ratio from 1:1 to 1:0.25.
Concentrates or masterbatches used to prepare the above-described compositions are also claimed herein. The concentrates comprise 20 to 60 weight percent propylene polymer carrier resin selected from the group consisting of propylene homopolymer, propylene copolymer and mixtures thereof and 40 to 80 weight percent additives comprising an organically modified smectite clay that has been ion-exchanged and intercalated with a quaternary ammonium compound of the formula:
(R)n(CH3)mN+Clxe2x88x92
where R represents a hydrogenated tallow moiety, n is 1 to 4, m is 0 to 3 with the proviso that n+m=4; and a propylene polymer compatibilizing agent obtained by copolymerizing or grafting 0.1 to 8 weight percent ethylenically unsaturated carboxylic acid or derivative monomer and 95 to 99.9 weight percent propylene, the weight ratio of organically modified clay to compatibilizing agent ranging from 1:5 to 1:0.1. Preferably, the carrier resin is polypropylene homopolymer. Especially useful concentrates contain 20 to 50 weight percent carrier resin and 50 to 80 weight percent organically modified clay and compatibilizing agent present at a weight ratio from 1:1 to 1:0.25 with up to 5 weight percent other conventional compounding additives.
In accordance with the present invention there is provided propylene polymer compositions, also referred to as composites, having increased melt strength as a result of using specific organoclay/compatibilizer combinations. Moreover, with the compositions of the invention it is possible to achieve the desired melt strength improvement and improve other physical properties utilizing significantly lower levels of compatibilizer and lower ratios of compatibilizer to organoclay than heretofore considered possible.
The increased melt strength or melt elasticity of the inventive compositions is evidenced by a noticeable upturn at low frequencies in their dynamic rheological data. By upturn is meant that the dynamic complex viscosity increases with decreasing frequencies at frequencies of less than about 1.0 rad/sec. In contrast, the propylene polymer base resins generally exhibit a limiting constant value at frequencies of about  less than 0.1 rad/sec. This complex viscosity upturn, which is measured in terms of xcex94G0*, is an indication that the composites of the invention have superior melt strength compared to the base resins. Enhanced melt strength is also indicated by high complex viscosities (xcex7*) at low frequencies. The relative increase in complex viscosity of the composite as compared to the base resin is expressed by the ratio of complex viscosity of the composite to the base resin at a frequency of 0.1 radians/second.
xcex94G0* is the difference, i.e., increase, in G0* obtained for the composite material over the G0* value observed for the propylene polymer base resin. It can be expressed by the equation:
xcex94G0*,=(G0*)compositexe2x88x92(G0*)base resin
xcex94G0* is expressed in dynes/cm2.
In general, the higher the xcex94G0* value, the greater the improvement in melt strength of the composite over the base resin. The procedure used to measure the Theological properties of the base resins and composites and determine the viscosity upturn is detailed in the examples.
As will be recognized by those skilled in the art, specific xcex94G0* values referred to herein are provided only to demonstrate the viscosity upturn, i.e., melt strength increase, obtained for the composites of the invention and are not intended to be limiting since they are generated under a specific set of conditions. Rheological data generated using different conditions, e.g., temperature, percent strain, plate configuration, etc., could result in xcex94G0* and complex viscosity ratio values which are higher or lower than those recited in the specification and claims which follow.
The invention is adaptable for use with any of the widely known and commonly used thermoplastic propylene polymer resins which includes homopolymers, copolymers and blends thereof. Copolymers can include random, block and impact copolymers where propylene is the major, i.e., greater than 50 weight percent, monomer constituent. Comonomers can include ethylene and C4-8 xcex1-olefins. Polypropylene homopolymer and random, block and impact copolymers of propylene and ethylene are particularly useful. The propylene polymer blends can be produced by physically blending two or more propylene polymers or they may be reactor-produced blends.
Useful propylene copolymers will contain 55 to 99.5 weight percent propylene and 0.5 to 45 weight percent ethylene. Even more preferred propylene polymer compositions comprise 65 to 99.5 percent propylene and 0.5 to 35 percent ethylene. These weight percentages are for the overall propylene polymer compositions, so that if the composition is comprised of two or more different propylene polymer components, the monomer contents of the individual polymer components comprising the blend may be outside the specified ranges.
A highly useful embodiment utilizes propylene-ethylene copolymers comprised of two phasesxe2x80x94a continuous phase of highly isotactic polypropylene homopolymer and a dispersed phase of rubber-like propylene-ethylene copolymer. Depending on the relative proportion of the continuous and disperse phases, these compositions are classified as either impact copolymers or thermoplastic polyolefins (TPOs)xe2x80x94the latter having a significantly higher rubber/elastomer content. Ethylene contents of these polymers will generally range from about 8 weight percent up to about 30 weight percent.
While these types of products can be produced by melt compounding individual polymer components, existing multi-reactor technology makes it possible to directly produce these products. This is conveniently accomplished by polymerizing. propylene in a first reactor and discharging the polypropylene homopolymer from the first reactor into a secondary reactor where propylene and ethylene are copolymerized in the presence of the polypropylene. Gas-phase polymerizations of this type are described in the article by Ross, et al., xe2x80x9cAn Improved Gas-Phase Polypropylene Process.xe2x80x9d Ind. Eng. Chem. Prod. Res. Dev. 1985, 24, 149-154.
Typically, in a first reactor, propylene is homopolymerized or it can be copolymerized with a C3-8 xcex1-olefin at a temperature from 50xc2x0 C. to 100xc2x0 C. and pressure from 250 psig to 650 psig utilizing a titanium catalyst and an organoaluminum cocatalyst. The highly isotactic homopolymer or copolymer produced in the first reactor is then directly fed into a second reactor typically maintained at 25xc2x0 C. to 80xc2x0 C. and 100 psig to 500 psig where propylene and ethylene are copolymerized in the presence of the polymer from the first reactor. The amount of ethylene employed in the second reactor is sufficient to produce a copolymer of propylene and ethylene with rubber-like characteristics. Polymerization in the second reactor is generally accomplished without additional catalyst; however, it may be advantageous, to introduce more catalyst to the second reactor. If more catalyst is employed, it can be the same as the catalyst used in the first polymerization or different.
High activity titanium catalysts, activated by contacting with an organoaluminum cocatalyst, are generally utilized for the gas-phase polymerizations. The polymerizations are carried out in the substantial absence of liquid reaction medium and gas velocity within the stirred-bed is maintained below the onset of fluidization. Depending on their compositional makeup, gases can be recirculated through external heat exchangers for cooling or partially condensed. Cooled monomer is recirculated into the reactor and provides thermal control. Recirculated monomer vaporizes when it is introduced into the reactor so that polymerization occurs in the gas phase. In the preferred mode of operation, i.e., stirred, fixed-bed gas phase, the first and second reactors are fitted with spiral agitators to maintain a turbulent mechanically fluidized bed of polymer powder and prevent agglomeration. Hydrogen is generally included in both reactors for control of molecular weight. The amount of hydrogen can range from 0.1 up to about 10 mole percent.
Each reactor typically has its own control system(s) and is capable of independent operation. In the usual conduct of the process, propylene and ethylene monomers are passed through desiccant beds prior to introduction. Means are usually provided to individually meter the propylene, ethylene, hydrogen for molecular weight control, catalyst and cocatalyst. This makes it possible to more readily control and maintain the desired reactor conditions. If desired, monomer may be injected into the recirculated gas stream for introduction into the system. Suitable controls are also provided to vary the pressure, temperature and compositional analysis to facilitate maintaining a constant environment in the reactor and/or to permit adjustment of conditions to bring the system into conformance. Residence times in both reactors are generally on the order of 1 to 4 hours.
Organoclays employed for the invention are smectite-type clays which have been modified by reacting the clay with a quaternary ammonium compound. The resulting cation exchanged clay, due to the incorporation of organic cations between the layers of the clay, exhibits organophilic character and facilitates dispersion in the propylene polymer resin.
Organoclays used for the invention are derived from smectite clays. Smectite clays are well known in the art as are the methods for modification with quaternary ammonium compounds. Representative smectite clays which can be employed include montmorillonite, bentonite, hectorite, saponite, beidellite and the like. Of these clays, montmorillonite clays and, more particularly, montmorillonite clays having an exchange capacity of at least 50 milliequivalents per 100 grams of clay are preferred.
For the purpose of this invention, clays of the above types and particularly montmorillonite clays, are reacted with a quaternary ammonium compound derived from tallow. More specifically, the quaternary ammonium compound corresponds to the formula:
(R)n(CH3)mN+Clxe2x88x92
where R represents a hydrogenated tallow moiety, n is 1 to 4, m is 0 to 3 and n+m=4. The tallow moiety, being derived from a natural product, is a mixture of aliphatic radicals typically comprised of predominantly C14-18 carbon atoms. The carbon number range and distribution within the carbon number range, i.e., percentage of each component, can vary within limits and will generally be those of tallow fatty acids which are generally derived from beef tallow or mutton tallow. Accordingly, the alkyl substituents will vary depending on factors such as the tallow source, treatment and age of the tallow. Typical values have, however, been generated and are as follow:
Source: CRC Handbook of Chemistry and Physics, 74th ed. (1993-94), pages 7-29.
When hydrogenated, even allowing for variations in tallow composition referred to above, it is expected that C16-18 alkyl substituents will comprise at least 80% by weight and, more typically, at least 90% by weight of the R groups. More specifically, it is anticipated R will be comprised of approximately 5% C14, 30% C16, and 65% C18 alkyl groups.
Montmorillonite clays modified with dimethyl dihydrogenated tallow ammonium chloride (abbreviated 2M2HT) and represented by the formula:
where HT represents the hydrogenated tallow group are particularly effective for the invention. Furthermore, modified clays of this type are available from commercial sources at different modifier concentrations. For example, Southern Clay Products, Inc., offers three montmorillonite clay products modified to different levels with 2M2HT, namely Cloisite(copyright) 6A with a modifier concentration of 140 meq/100 g, Cloisite(copyright) 15A with a modifier concentration of 125 meq/100 g and Cloisite(copyright) 20A with a modifier concentration of 95 meq/100 g. While all three of these modified clays can be employed for the invention, montmorillonite clay modified with 2M2HT at a concentration of 95 meq/100 g is particularly advantageous.
A compatibilizing agent which is a polymer of propylene containing about 0.1 to 8 weight percent ethylenically unsaturated carboxylic acid or derivative monomer either copolymerized or grafted is included with the propylene homopolymer or copolymer and organically modified clay in order to obtain the improved composites of the invention. As used herein the term xe2x80x9cgraftingxe2x80x9d denotes covalent bonding of the grafting monomer to the polymer chain of the propylene polymer.
The monomer is at least one polymerizable, ethylenically unsaturated carboxylic acid or acid derivative monomer, such as an acid anhydride, ester, salt, amide, imide, or the like. Such monomers include but are not limited to the following: acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, maleic anhydride, 4-methyl cyclohex-4-ene-1,2-dicarboxylic acid anhydride, bicyclo(2.2.2)oct-5-ene-2,3-dicarboxylic acid anhydride, 1,2,3,4,5,8,9,10-octahydronaphthalene-2,3-dicarboxylic acid anhydride, 2-oxa-1,3-diketospiro(4.4)non-7-ene, bicyclo(2.2.1)hept-5-ene-2,3-dicarboxylic acid anhydride, maleoprimaric acid, tetrahydrophthalic anhydride, norborn-5-ene-2,3-dicarboxylic acid anhydride, Nadic anhydride, methyl Nadic anhydride, Himic anhydride, methyl Himic anhydride, and x-methylbicyclo(2.2.1)hept-5-ene-2,3-dicarboxylic acid anhydride (XMNA).
Maleic anhydride is a preferred monomer for preparation of the compatibilizing agents of the invention. It is particularly advantageous when the maleic anhydride is grafted on the propylene polymer. When the ethylenically unsaturated carboxylic acid or acid derivative monomer is grafted, and particularly when grafting maleic anhydride, the propylene polymer will preferably contain about 0.2 to 2.5 weight percent of the grafting monomer.
The modified, i.e., copolymerized or grafted, propylene polymer compatibilizing agents useful for the invention are comprised predominantly of propylene units grafted or copolymerized with the ethylenically unsaturated carboxylic acid or acid derivative monomer. Other olefinic hydrocarbon monomers may be present with the propylene and ethylenically unsaturated carboxylic acid or acid derivative monomer; however, these will generally constitute less than 35 weight percent and, more typically, less than 25% of the polymer composition. Ethylene and C3-8 xcex1-olefins are most commonly used comonomers with propylene for the compatibilizing agents. It is particularly advantageous when the compatibilizing agents are obtained by polymerizing propylene and ethylene with ethylenically unsaturated carboxylic acid or acid derivative monomer or by grafting a propylene-ethylene copolymer with ethylenically unsaturated carboxylic acid or acid derivative monomer. It is even more advantageous where ethylenically unsaturated carboxylic acid or acid derivative monomer is maleic anhydride.
Whether copolymerized or grafted, the ethylenically unsaturated carboxylic acid or acid derivative monomer will be incorporated with the propylene monomer (and other comonomers, if present) or, in the case of grafting, the propylene homopolymer or copolymer in accordance with conventional procedures known to those skilled in the art.
For example, grafted propylene polymer compatibilizers may be prepared in solution, in a fluidized bed reactor, or by melt grafting. Particularly useful modified products are conveniently prepared by melt blending the propylene polymer, in the substantial absence of a solvent, with a free radical generating catalyst, such as a peroxide, and the grafting comonomer using a shear-imparting reactor, such as an extruder reactor. Twin screw extruders, such as those marketed by Werner-Pfleiderer, are especially useful for melt grafting. Since substantial amounts of solvent are to be avoided, the catalyst and graft monomer are preferably added directly to the reactor.
Graft reactions are typically carried out temperatures above the decomposition temperature of the free radical generating catalyst; however, excessive temperatures should be avoided to minimize or avoid rapid vaporization and consequent losses of the catalyst and graft comonomer. A temperature profile where the temperature of the polymer melt is increased over the length of the extruder up to a maximum in the reaction zone and then decreases toward the extruder output is preferred. Temperature attenuation facilitates processing of the resulting modified product for pelletization or the like. When using maleic anhydride and di-tert-butyl peroxide, a preferred free radical initiator, operating temperatures within the extruder generally range from 190xc2x0 C. up to 215xc2x0 C.
The grafted propylene polymers have melt flow rates (MFRs) greater than that of the propylene polymer before grafting. Whereas MFRs of the grafted propylene polymer, i.e., compatibilizing agent, may range from about 10 to 1000 g/10 min, the MFR is most generally in the range 40 to 400 g/10 min. MFRs (to be distinguished from melt indexes) are determined in accordance with ASTM D-1238, Condition L (230xc2x0 C.; 2160 g; 0.0825 in capillary).
In general, the same types of propylene polymers that can be employed as the base resin for the composite compositions can be grafted and used as the compatibilizing agent. This includes propylene homopolymers and propylene copolymers including random, block and impact copolymers as well as blends of these polymers.
The thermoplastic resin compositions of the invention, i.e., composites are prepared by melt compounding the ingredients. Prior to melt compounding all or a portion of the components may be dry blended to facilitate operation. Also, a concentrate or masterbatch containing the modified clay and/or compatibilizing agent and any other additives, such as antioxidants and the like, may be utilized to facilitate mixing with and incorporation in the propylene polymer base resin. The composite materials may be used directly as obtained from the melt compounding operation or, as is more commonly the case, the products may be stored for subsequent use. When the composites are to be retained, they are typically pelletized or put in some other form suitable for handling.
The use of concentrates to effectively incorporate compounding ingredients into polypropylene resins is well known. This procedure is also useful since it minimizes the number of materials which must be stored and handled by processors. The procedure involves preparing a concentrate, i.e., masterbatch, having relatively high concentrations of modified clay and compatibilizing agent (and any other optional additives) and present in the appropriate ratios using a carrier resin in which the additives are readily dispersed and which is compatible with the xe2x80x9cend-usexe2x80x9d propylene polymer base resin. Typically, the carrier resin used for the concentrate will be the same as the end-use resin or will be a resin from the same polymer family, but possibly having better processability than the end-use resin. The concentrate, typically in pellet form or some other form suitable for handling, is then xe2x80x9cletdownxe2x80x9d into the propylene polymer base resin to achieve the desired level of organoclay, compatibilizer and other additives desired in the final product.
Concentrates utilized for the present invention generally utilize propylene homopolymer or copolymer, which may be the same or different than the base resin, as the carrier resin. Polypropylene homopolymers are particularly advantageous carrier resins. The concentrates will contain 20 to 60 weight percent carrier resin and 40 to 80 weight percent additive components, which includes the modified clay and compatibilizing agent and, if present, any other optional additive components. The above weight percentages are based on the total concentrate. Especially useful concentrates are comprised of 20 to 50 weight percent carrier resin and 50 to 80 weight percent additive components. The weight ratio of modified clay to compatibilizing agent in the concentrate will be the same as specified for the composites.
The composites are comprised of from 76 to 99 percent of the propylene homopolymer or copolymer base resin with 0.5 to 12 percent of the organically modified clay and 0.5 to 12 percent of the propylene polymer compatibilizing agent. All of the above percentages are weight percentages and are based on the weight of the total composition. Additionally, the weight ratio of organically modified clay to compatibilizer will range from about 1:5 to 1:0.1. Especially useful compositions will contain 84 to 98.75 percent propylene homopolymer or copolymer, 1 to 8 percent organically modified clay and 1 to 8 percent of the compatibilizing agent. Preferred composites have a weight ratio of clay to compatibilizer from 1:1 to 1:0.25.
Conventional compounding additives commonly included in propylene polymer compositions may also be included in the composites of the invention; however, they typically will be present in a combined amount of less than 5 weight percent and, more typically, the total concentration of all additives will not exceed 2 weight percent. Representative additives, which may be optionally included are heat stabilizers, antioxidants, processing aids, nucleating agents, colorants, clarifiers, UV stabilizers, acid scavengers and coupling agents, such as silanes. Additionally, conventional fillers such as talc, can also be employed in which case the total amount of optional additives may be as high as 30 weight percent.
Composites produced in accordance with the invention having improved melt strengths will have MFRs generally in the range 0.1 to 100 g/10 min and, more preferably from 0.25 to 75 g/10 min. xcex94G0* values will typically be greater than 50 dyne/cm2. Complex viscosity ratios at low frequency (0.1 radians/sec) are greater than 1.1.
In addition to having enhanced melt strength, composites produced in accordance with the invention can exhibit other improved physical properties compared to compositions prepared using other organically modified clays and compatibilizing agents. For example, improved stiffness and heat distortion may also be obtained with the composites of the invention.
The composites of the invention may be advantageously used for a variety of applications including thermoforming, blow molding, extrusion coating and foamed and sheet extrusion and eliminate many of the problems heretofore observed when processing propylene polymer resins. For example, in blow molding applications the lack of melt strength in conventional polypropylene resins leads to reduced parison hang times, especially when blow molding larger parts which require larger parisons. The upturn in complex viscosity and corresponding increase in melt strength obtained with the composites of the invention increase parison hang times thereby improving the blow molding operation. Also, in thick (0.25-1.5 inch) sheet extrusion processes where conventional polypropylene resins have a tendency to sag as they exit the die and before they contact the chill roll, use of the composite materials of the invention can eliminate or at least significantly reduce sagging and any operational problems associated therewith. Similar advantages over conventional propylene polymer resins are obtained when the composites of the invention are utilized in thermoforming and extrusion coating processes.
The following examples are given to illustrate the scope of the present invention. Because these examples are given for illustrative purposes only, the invention embodied therein should not be limited thereto.
In these examples, Theological properties were determined using a Rheometrics ARES rheometer. Rheological data were generated by measuring dynamic rheology in the frequency sweep mode to obtain complex viscosities (xcex7*), storage modulus (Gxe2x80x2) and loss modulus (Gxe2x80x3) for frequencies ranging from 0.0251 to 398 rad/sec for each composition. The rheometer was operated at 210xc2x0 C. in the parallel plate mode (plate diameter 50 mm) in a nitrogen environment (in order to minimize sample oxidation/degradation). The gap in the parallel plate geometry was 1.2-1.4 mm and the strain amplitude was 10 percent (except where noted otherwise). Rheological properties were determined using standard test procedure ASTM D 4440-84.
The measure of viscosity upturn, xcex94G0* of each composite was determined from the rheological data using a modified Casson plot of G* vs. xcfx89 wherein G* is the absolute value of dynamic modulus and xcfx89 is the frequency. The five lowest frequency points for each data set were used to obtain an intercept value G0* at xcfx89=0 by the linear extrapolation method. xcex94G0* is the difference in G0* between the composite and the base resin. It is a measure of the upturn, i.e., increase, in complex viscosity of the nanocomposite materials of the invention.
In all of the examples, the organoclay and compatibilizing agent were incorporated into the propylene base resin utilizing a masterbatch procedure. Materbatches/concentrates contained 50 weight percent modified clay and the appropriate amount of compatibilizing agent, depending on the ratio of modified clay to compatibilizing agent desired. The balance of the concentrate for Examples 1, 2, 13 and 14 and comparative examples A, B, C and D was a 0.7 MFR polypropylene homopolymer carrier resin containing 1000 ppm Irganox(copyright) 1010, 1000 ppm Irganox(copyright) 168, 1000 ppm calcium stearate and 500 ppm dihydrotalcite. For all other examples and comparative examples, the carrier resin was an in-reactor produced propylene-ethylene (11.5%) copolymer having an MFR of 1.6 and containing 1000 ppm Irganox(copyright) 626, 1000 ppm Ultranoxe(copyright) 626 and 750 ppm calcium stearate. When a silane coupling agent was used, the silane was first added to the modified clay and this mixture then dry blended with the carrier resin (except in comparative examples B and D, where a commercially produced silane pretreated clay was used). The modified clay/carrier resin mixture was then fed into a twin screw extruder along with a side feed of the compatibilizing agent. The strand of molten concentrate exiting the extruder was pelletized in an underwater pelletizer.
To prepare the composite, the appropriate amount of the concentrate pellets were dry blended with pellets of the base resin and compounded on the twin screw extruder. For example, to obtain a composite containing 88% base resin, 6% modified clay, 3% compatibilizing agent and 3% carrier resin 12 parts concentrate (having a weight ratio of modified clay to compatibilizing agent of 1:0.5) was let down into 88 parts base resin.
A ZSK-30 twin screw extruder (30 mm screw diameter; L/D 38.7) was utilized for processing both the masterbatch and composite. The temperature profile of the extruder was as follows:
Materials employed for the examples were as follows:

Propylene polymer composites having improved melt strength


The beaver control screen has a cone-shaped screen having a base, an apex and a horizontal axis. A first set of spaced-apart rods extends from the base to the apex and are disposed in a first conical layer. A second set of rods is disposed in a second conical layer inside the first conical layer and extends toward the apex over a distance of about one-half the length of the first conical layer. The first and second conical layers are set at different angles with the horizontal axis such that a distance between a rod in the first layer and an adjacent rod in the second layer is a same distance along the adjacent rod. At the apex of the screen, the rods in the first conical layer are alternately affixed to the outside edge and to the inside edge of an annular plate.

This invention pertains to a cone-shaped screen for attachment to the end of a culvert pipe for preventing beavers from constructing a dam upon the end of, or inside the culvert pipe. More particularly, the present invention pertains to a double layered cone-shaped screen with aperture dimensions selected to refuse access to beavers and to let local fish and floating debris there through.
A culvert pipe along a stream represents an ideal flow restriction upon which a beaver can build a dam. In periods of rising water due to heavy rains or melting snow for example, such dams are known to cause road flooding and road undermining which often result in extensive damage. Road maintenance personnel usually try to dismantle a beaver dam at an early stage of its construction. As part of the dismantling process, the beavers are trapped and re-located in deeper forests. This relocation of the animals is a temporary solution because other beavers usually come along and start all over. Therefore it is preferable to install permanent screens over the ends of a culvert pipe in which flows an active brook or stream, to discourage any beaver from attempting to construct a dam at that location.
Certain types of screens or grates mounted over the end of a culvert pipe are known to be efficient devices for discouraging beavers from building a darn. However, such screens or grate must be made so that the flow of water through the culvert pipe, in all seasons, is not adversely affected. Similarly, the circulation of the local fish through the screen must be maintained such that the natural fish habitat is not disturbed. It is believed that these two particular requirements for an efficient beaver control screen represent some challenges and have not been properly addressed in the past.
It is known that several types of beaver control screens and grates have been developed and used in the past with varying degrees of success. Some of these inventions are described herein below.
The first type of culvert pipe screen of the prior art consists of a wire strainer mounted inside the pipe, to prevent rodents from entering the pipe and freely circulating inside the pipe. Culvert pipe screens of this type are described in the following patents:
U.S. Pat. No. 906,562, issued on Dec. 15, :1908 to C. S. Rue et al.;
U.S. Pat. 5,090,152, issued on Feb. 25, 1992 to R. Ling.
A second type of screen consists of a grating mounted over the end of a culvert pipe. The grating has a flat surface and is made of parallel and perpendicular bars affixed to each other and to the pipe. Some of these screens are described in the following patents:
U.S. Pat. No. 3,587,239, issued on Jun. 28, 1971 to O. A. Feland;
U.S. Pat. No. 5,037,542, issued on Aug. 6, 1991 to K. T. Carroll;
U.S. Pat. No. 4,713,179, issued on Dec. 15, 1987 to S. J. Goedderz, Sr.;
CA Pat. No. 1,234,766, issued on Apr. 5, 1988 to E. B. Piercy et al.
The prior art also contains a cylindrical screen made of wire mesh and which completely encloses the upstream end of a culvert pipe. An example of this type of culvert pipe screen is described in:
CA Pat. No. 1,290,578, issued on Oct. 15, 1991 to N. J. Thurber.
Although several solutions have been proposed to the problems caused by beavers near culverts, it is believed that the prior art systems and devices are deficient in at least several important features. For example, some of the bars or rods of the screen are perpendicular to the flow of water and promote the accumulation of floating debris against the surface of the screen. A clogged screen on the end of a culvert pipe has a similar effect as a beaver dam, as the water accumulating at that location could also cause road flooding and road undermining. Also, a flat screen mounted over the end of a culvert pipe, or inside the pipe, does not prevent a beaver from anchoring a dam on the end of the culvert pipe. Therefore, flat screens are not considered to be an efficient solution to control beaver problems.
The deficiencies of flat screens have prompted other inventors to develop cone-shaped screens which extend away from the end of the culvert pipe and which are more efficient in preventing access to the end of the culvert pipe to a beaver. The cone-shaped screen normally makes an acute angle with the water currents and is therefore less susceptible to clogging. A cone-shaped screen also has a large surface as compared to the cross-section area of the culvert pipe on which it is mounted, and therefore more debris is required to clog it.
Therefore, the type of beaver control screen which is of interest herein has a conical shape and is secured to either end of a culvert pipe. Some examples of conical screens of the prior art are described in the following documents:
U.S. Pat. No. 2,970,697, issued on Feb. 7, 1961 to E. L. Larson et al.;
U.S. Pat. No. 3,472,030, issued on Oct. 14, 1969 to R. E. Rieke;
U.S. Pat. No. 5,102,537, issued on Apr. 7, 1992 to J. R. Jones;
CA Pat. No. 208,647, issued on Feb. 22, 1921 to L. H. Bradburn.
However, a conical screen has rods or bars which converge toward the apex thereof. When the cone-shaped screen is installed on the downstream end of a culvert pipe, these converging rods, with the force of water, act as a trap where fish can become caught. Therefore, the converging rods of cone-shaped screens are not recommended as they could eventually destroy the local fish population.
As such, it may be appreciated that there continues to be a need for a new and improved beaver control screen for installation on culvert pipes, which can be efficiently used to discourage the construction of beaver dams, which does not clog easily and which does not hinder the migration of local fish there through.
The beaver control screen according to the present invention has three main purposes. Firstly, the beaver control screen is made to protect the entire culvert against damages caused by debris transported by water, especially,during spring thaw periods and during heavy rainstorms. Secondly, the present invention is made to efficiently prevent beavers from building a dam on the end of a culvert pipe or inside a culvert pipe. Thirdly, the beaver control screen is made to preserve the natural fish habitat.
In accordance with a first aspect of the present invention, there is provided a beaver control screen comprising a cone-shaped screen having a base, an apex and a central horizontal axis and a length between the base and the apex. The cone-shaped screen has a first set of spaced-apart straight rods extending from the base to the apex and being disposed in a first conical layer. A second set of spaced-apart straight rods is disposed in a second conical layer inside the first conical layer and extends toward the apex over a distance of about one-half the length of the first conical layer. The second conical layer is disposed in a concentric relationship with the first conical layer. Each rod in the first conical layer is spaced away from an adjacent rod in the second conical layer a same spacing of about 3 inches along this adjacent rod. This spacing has been found to be advantageous for preventing access to the culvert pipe to adult and juvenile beavers, and on the other hand, has been found to be relatively tolerant to the passage of floating debris through the screen.
A beaver dam is usually built using intertwined branches and twigs of various sizes, cemented with mud, lichen and other aquatic plants. The smooth surface of the rods and the spacing between the rods at the base of the beaver control screen according to the present invention prevent the beavers from building a foundation of branches and twigs across the opening of the culvert pipe.
According to another feature of the present invention, the apex of the cone-shaped screen is made with an annular plate having an outside edge and an inside edge. The rods in the first conical layer are alternately affixed to the outside edge and to the inside edge. In this arrangement, a minimum spacing between any two adjacent rods in the screen can be made to be larger than other prior art arrangements where all the rods are affixed to each other or to the outside edge of the apex plate for examples. In areas where local fish species such as the char, (Salvelinus), co-habit with beavers, the minimum spacing between the rods is made to be at least about 1.25 inches, such that the converging rods of the screen do not constitute traps which could threaten the survival of fish population.
In accordance with yet another feature of the present invention, the beaver control screen is affixed to the culvert pipe by means of a hinge on the upper segment of culvert pipe. The hinge has a horizontal articulation axis. The beaver control screen according to the present invention is simply tilted upward about the hinge to clear any debris that might accumulate on its surface.
Other advantages and novel features of the present invention will become apparent from the following detailed description.